We report a method of inducing antigen production in dendritic cells (DCs) by in vivo targeting with lentiviral vectors that specifically bind to the DC surface protein, DC-SIGN. To target the DCs, the lentivector was enveloped with a viral glycoprotein from Sindbis virus, engineered to be DC-SIGNspecific. In vitro, this lentivector specifically transduced DCs and induced DC maturation. A remarkable frequency (up to 12%) of ovalbumin (OVA)-specific CD8 + T cells and a significant antibody response were observed 2 weeks following injection of a targeted lentiviral vector encoding an OVA transgene into naïve mice. These mice were solidly protected against the growth of the OVA-expressing E.G7 tumor and this methodology could even induce regression of an established tumor. Thus, lentiviral vectors targeting DCs provide a simple method of producing effective immunity and may provide an alternative route for immunization with protein antigens.Immunization is one of the most productive tools in modern medical practice yet it still has limitations and novel methods of immunization are likely to be needed. 1 One of the great advances in our understanding of the process of immunization was the recognition of the role of dendritic cells (DCs) as specialized antigen-presenting cells (APCs). 2 This has led to attempts at DC-based immunization/vaccination involving loading DCs with specific antigens. 3, 4 Although significant progress has been made on various aspects of this vaccination method, many challenges still remain in order to rationally manipulate DCs to achieve protective immunity. [3][4][5] There is growing interest in genetically modifying DCs to make them either express antigens or produce immuno-stimulatory molecules. 6 Of these methods, viral vectors have been proven most effective for the delivery of genes into DCs in vitro. 7 The most popular viral vectors capable of transducing and expressing transgenes in DCs are adenoviral vectors, 8-10 gammaretroviral vectors 11, 12 and lentiviral vectors. [13][14][15] Considerable effort has also gone towards direct immunization using recombinant viral vectors as vaccine carriers. In these protocols, viral vectors are injected directly into an animal with the hope that a fraction will target immune cells and stimulate the desired immunity. Direct injection of adenoviral vectors was shown to induce both innate and adaptive immune responses and is currently being evaluated as a subunit vaccine for several infectious diseases and cancer. 16-18 Direct injection of lentivectors into mice does transduce DCs, leading to antigen-specific CD8 + T cell responses and anti-tumor immunity. 19-22 However, these 4Correspondence should be addressed to D.B. (baltimo@caltech.edu) or P.W. (pinwang@usc.edu). 3 These authors contribute equally to this work.
COMPETING INTERESTS STATEMENT:The authors declare that they have no competing financial interests. Here we report a new method of in vivo DC targeting through the DC-specific surface molecule called DC-SIGN (also known as CD209) ...